This invention relates to a floating deep water offshore apparatus or jacket spar for use in drilling and production of offshore wells for extended periods of time.
Prior proposed apparatus of spar type have included a long vertically disposed floating hull, body, or caisson with an upper structure above the water and a lower structure immersed in the water a selected depth. The upper structure is subjected to winds and currents and the lower structure is subjected to variable wave motion. Means to stabilize the apparatus against heave motion, pitching and roll motions have been proposed and have included the use of horizontally disposed areas vertically spaced along the longitudinal axis of the spar to modify the heave response of the apparatus. Such spacing was very great as shown in U.S. Pat. Nos. 3,404,413; 3,510,892. The use of relatively wide large horizontal surface areas to act as virtual mass trap means is described in U.S. Pat. No. 4,516,882 where the use of such areas is in connection with conversion between tension leg platform and semisubmersible modes. Such prior apparatus also included an anchor system in which mooring lines were connected with the lower portion of the hull structure and connected to anchor means in the sea floor in a gravity catenary mode or in a taut mode with the lines under tension. In some instances the bottom of the floating structure included ballast means.